This invention relates to a cylinder head for internal combustion engines, and more particularly to improvements in the arrangement of an exhaust gas recirculating passage in the cylinder head.
Exhaust gas recirculation systems are well known which returns part of exhaust gases emitted from an internal combustion engine to the intake system of the engine so as to lower the maximum combustion temperature within the cylinders of the engine, to thereby reduce the amount of nitrogen oxides (NOx) contained in the exhaust gases. In an internal combustion engine of the so-called crossflow type wherein the intake system and the exhaust system are arranged at diametrically opposite sides of each cylinder head, the cylinder head is formed therein with a cavity defining a combustion chamber in cooperation with a cylinder and a piston, an intake port located at one side of an axial plane extending through the diametrical center of the same cavity and axially of the crankshaft of the engine and communicating with the combustion chamber-defining cavity, an exhaust port located at the opposite side of the above axial plane and communicating with the combustion chamber-defining cavity, and an exhaust gas recirculating passage forming part of an exhaust gas recirculation system and communicating with the exhaust port. Part of exhaust gases emitted into the exhaust port is guided through the exhaust gas recirculating passage to a portion of the cylinder head at which an intake manifold is mounted, and further guided through a passage formed within the intake manifold to an exhaust gas recirculation control valve mounted in the intake manifold. The exhaust gas recirculation control valve operates in response to operating conditions of the engine to supply a suitable amount of exhaust gases through a passage extending in the manifold along a lateral wall thereof to an intake passage formed within the intake manifold, where the exhaust gases are mixed into the mixture. In this way, exhaust gas recirculation is carried out.
If exhaust gases are returned at an excessive rate and mixed into the mixture, there can undesirably occur a drop in the output of the engine, as well as unstable combustion of the mixture in the engine cylinders. However, in the aforementioned conventional cylinder head, an excessive amount of exhaust gases can frequently flow into the exhaust gas recirculating passage via a gasinlet end of the same passage which opens in the exhaust port, due to incessantly fluctuating flows of exhaust gases in the exhaust port, causing the above-mentioned inconvenience.
Furthermore, component parts of the exhaust gas recirculation system such as the exhaust gas recirculation control valve are exposed to the hot exhaust gases flowing in the exhaust gas recirculating passage, which can result in shortened effective life of the exhaust gas recirculation system.